The present invention relates to a non-invasive apparatus for detecting biological activities in a specimen such as blood, where the specimen and a culture medium are introduced into a large number of sealable containers and then exposed to conditions enabling a variety of metabolic, physical, and chemical changes to take place in the presence of microorganisms within the sample.
The presence of biologically active agents such as bacteria in a patient's body fluid, especially blood, is generally determined using blood culture vials. A small quantity of blood is injected through an enclosing rubber septum into a sterile vial containing a culture medium. The vial is incubated at 37.degree. C. and monitored for microorganism growth.
One of the techniques used to detect the presence of microorganisms includes visual inspection. Generally, visual inspection involves monitoring the turbidity or eventual color changes of the liquid suspension of blood and culture medium. Known instrumental methods detect changes in the carbon dioxide content of the culture bottles, which is a metabolic by-product of the bacterial growth. Monitoring the carbon dioxide content can be accomplished by methods well established in the art, such as radiochemical or infrared absorption at a carbon dioxide spectral line. Until now, these methods have required invasive procedures of the vial which results in the well-known problem of cross-contamination between different vials.
It has also been proposed to detect microorganism growth in sealable containers by monitoring positive and/or negative pressure changes.
Recently, non-invasive methods have been developed involving chemical sensors disposed inside the vial. These sensors respond to changes in the carbon dioxide concentration by changing their color or by changing their fluorescence intensity. (See, e.g., Thorpe, et al. "BacT/Alert: An Automated Colorimetric Microbial Detection System", J. Clin. Microbiol., July 1990, pp. 1608-12, and U.S. Pat. No. 4,945,060, Turner, et al., the disclosures of which are incorporated by reference). In known automated non-invasive blood culture systems, individual light sources, spectral excitation/emission filters, and photodetectors are arranged adjacent to each vial. This results in station sensitivity variations from one vial to the next. Therefore, extensive and time-consuming calibration procedures are required to operate such systems. In addition, flexible electrical cables are required to connect the individual sources and detectors with the rest of the instrument. With the large number of light sources, typically 240 or more per instrument, maintenance can become very cumbersome and expensive when individual sources start to fail.
In known colorimetric or fluorometric instruments, light emitting diodes ("LEDs") are used as the individual light sources. These sources have only a relatively low optical output power. Therefore, a high photometric detection sensitivity is required to monitor the vial sensor emissions. This results in additional and more complicated front-end electronics for each photodetector, increasing production cost. To reduce equipment cost and complexity, it has been proposed to use optical fibers at each vial to feed the output light of an instrument's sensors to a central photodetector. A disadvantage to this approach is the need for arranging a large number of relatively long fibers of different length within the instrument.
In known automated non-invasive blood culture systems, no vial identification is provided within the instrument. Instead, microbiology lab personnel are required to execute a manual log-in for each vial. Besides being time-consuming, this step generates a certain probability for mistakes.